Data transfers to and from users are becoming an increasingly important and used feature of Code Division Multiple Access (CDMA). Users of wireless devices, such as wireless phones and wireless laptops, are using the devices to receive and transfer large amounts of data, including documents, web pages, and e-mail. As demand for this feature grows, however, existing network elements and equipment are pushed to their limits. One particular problem with data transfers is the management of the limited amount of power available for CDMA users.
CDMA is a low-powered technology that ensures quality by utilizing a broad spectrum broadcast. A typical wireless communications network consists of a Base Station Controller (BSC) connected to at least one Base Transceiver Station (BTS). Each BTS comprises a radio antenna, with at least one sector, but typically three. Each sector is capable of transmitting to and receiving from a plurality of Mobile Stations (MSs), which consists of wireless devices such as wireless phones or wireless laptops. The number of users that any given sector is capable of supporting at any moment is dependent, among other things, the amount of power available to the BTS.
A BTS has a limited amount of power for transmitting within any sector, typically 12-18 Watts (W). Out of the total amount of power available, a reserve, typically 25%, is normally allocated to overhead and is not available to users. The remaining power is available to users for voice and data communications.
Under prior standards, such as IS-95, whether or not the BTS had sufficient power to complete the transfer was easily determined. Transfers, both voice and data, were performed over a single channel, the Fundamental Channel (FCH), at a fixed transfer rate of either 9.6 or 14.4 kilobits per second (kbps). Since the average amount of power required per sector to transmit at a given rate to any two users is approximately equal, every channel had approximately the same power requirement. To determine the amount of power required, the BSC would simply calculate the average power per FCH by dividing the total amount of power consumed by existing FCH users, by the number of FCH users. If the sector had sufficient power available for the new user, the transfer would be initiated. Otherwise, the transfer would be rejected.
Until the advent of IS-2000, multiple FCH channels were allocated to a single user to achieve a faster rate of transfer. IS-2000, however, provides variable rate data transfers within a single channel. Users are still allocated a fixed 9.6 kbps FCH but are also allocated a variable rate Supplemental Channel (SCH). The SCH is capable of transmitting data at rates of 9.6-307.2 kbps. The optimum power level, however, varies with the data transfer rate. Therefore, the method used to predict the availability of power used for IS-95 systems is not suitable for IS-2000 systems. The amount of power required by the SCH must be adjusted to prevent an inefficient use of the available power.
Another problem with IS-2000 is that the BSC must set the initial target signal-to-noise ratio, referred to as Eb/N0, where Eb represents the energy per information bit and N0 represents the power spectral density of interference. This value is used to initialize an outer power control loop at the mobile station (MS). The outer power control loop is a mechanism, commonly known in the art, in which the MS continually updates the target Eb/N0, which is used in the inner power control loop to compare to the measured Eb/N0. The comparison is used to generate fast power control feedback. This method is used to achieve the optimum amount of power without creating undue interference to other users or experiencing an unacceptable level of frame errors.
If the initial Eb/N0 is not set correctly, inefficiencies will result. First, if the initial Eb/N0 is set too large, the BTS will send the data with too much power. This results in wasted power (less available power to other users) and interference (increased power of one user increases power of another user in order to overcome interference introduced by the first user) to other users. Second, if the initial Eb/N0 is set too small, the transmission will be delayed as the power will not be sufficient for the MS to receive, or the user will experience a series of frame errors until the power is raised to a sufficient level.
Therefore, what is needed is a method for analyzing the initial power requirements for a given data transfer request and initializing the outer power control loop, thereby allowing for greater efficiencies and increased capacity in the system.